JPH02244707A - Projection exposure face illuminance distribution measuring method, and exposure face illuminance distribution compensating method, and projection exposer - Google Patents

Abstract

PURPOSE:To measure the illuminance distribution in projection exposure meeting the conditions of real exposure so as to improve the line width accuracy and linearity of a pattern formed on a substance (substrate) to be exposed and to make resist film uniform by measuring the illuminance distribution of the face to be exposed, in the conditions where the light receiving face of a light receiver is put in the same conditions as the light reflecting conditions on a substrate being the target of exposure and a reticle is actually mounted. CONSTITUTION:Exposure illuminance distribution at a position corresponding to the wafer face is compensated from measured data. To begin with, a first filter 31 is formed, which is to be compensated on the basis of the illuminance distribution measured data being monitored. The filter 31 is to remove the swelling at the center of illuminance distribution 24 during actual exposure, and the light transmissivity is made rather lower at the center than at the periphery, and the light transmissivity at the center is determined on the basis of illuminance distribution measured data. By existence of this optical filter 31, the light intensity distributions 34 and 36 on an integrator 3 and an incident pupil 7 of a reduction lens 6 become distributions that the centers are recessed as shown by the figure. The recess of this light intensity distribution offsets the swelling of light intensity arising at the center or its vicinity of exposure illuminance distribution 24 equivalent to real time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for measuring illuminance distribution on an exposed surface in projection exposure, a method for correcting illuminance distribution, and a projection exposure apparatus.

[Conventional technology]

Projection exposure techniques such as reduction projection exposure are used, for example, in photolithography processes for semiconductor manufacturing. When performing this type of projection exposure, there is a need to improve dimensional accuracy within the field and uniformity of film loss, and optimization of the exposure light illuminance distribution on the wafer surface (flattening) is directly related to this requirement.
It is necessary to aim for Therefore, the I projection exposure apparatus incorporates an optical element (for example, a condenser lens) that flattens the illuminance distribution of the exposure light beam to some extent.

In addition, when measuring the illuminance distribution in the exposed area,
Conventionally, it has been common to remove the resist-coated wafer or the reticle, which serves as the original pattern, from the apparatus before making measurements. The reason for removing the wafer is due to the working distance of the reduction projection lens (the distance between the lowest end surface of the reduction lens and the wafer is small), and the reason for removing the reticle is to select a standard reticle from among the many available. This was thought to be because it was difficult to decide.

Here, a specific example of conventional reduction/J% projection exposure and illuminance measurement will be explained based on FIGS. 4 and 5.

In Fig. 4, 1 is a condenser mirror, 2 is a mercury lamp as a light source, 3 is an integrator, 4 is a condenser lens, 5 is a reticle that is the original pattern, 6 is a reduction lens, 7 is the entrance pupil of the reduction lens, 8 is a wafer, 9 is a wafer chuck,
10 is an X stage, 11 is a Y stage, and 12 is an X stage.

The wafer 8 is held by a wafer chuck 9, and the wafer chuck 9 is held on the xyz stages 12, 11, and 10 by vacuum suction. 13 is a motor for moving the X stage, 14 is a motor for moving the Y stage, and 15 is a motor for moving the X stage.

The light from the mercury lamp 2 is collected by a condenser mirror 1, passes through an integrator 3, and is uniformly illuminated onto the surface of a reticle 5 by a condenser lens 4. Then, the light that has passed through the reticle 5 is guided onto the incidence [7] of the reduction lens 6. The reduction lens 6 uses the surface facing the reticle 5 as an object surface, and the surface of the wafer 8 coated with a resistor as an image surface. Therefore, the pattern drawn on the reticle 5 is transferred onto the wafer 8 surface.

A light receiver 16 is installed on the second stage 10 so as to be located next to the wafer chuck 9 for measuring the illuminance distribution at a position corresponding to the eight surfaces of the wafer.

Next, the determination of the illuminance distribution H1ff using the light receiver 16 will be explained.

When measuring the illuminance distribution at a position corresponding to the exposed surface, remove the reticle 5 as shown in FIG.

Also, move the stage in the XY direction so that the light receiver 16 is in the light irradiation area.
The light illuminance distribution was measured by controlling the force direction and controlling the position of the stage in the Z direction so that the surface of the light receiver 16 was at the same height as the surface of the wafer 8.

In addition, on the surface of the light receiver 16, in order to improve the light absorption sensitivity,
Its top surface is black-treated.

Furthermore, the measurement of illuminance distribution as described above has conventionally been carried out only to check whether the illuminance distribution on the exposed surface has been approximately flattened using a condenser lens, etc., and is based on this illuminance distribution measurement data. Therefore, no consideration was given to further actively correcting the illuminance distribution. A conventional technique for a projection exposure apparatus is disclosed in, for example, Japanese Patent Laid-Open No. 59-43324.

[The problem that the invention attempts to solve]

By the way, as mentioned above, when the illuminance distribution of a projection exposure system is measured without a process wafer or reticle, the wafer and reticle during actual exposure (projection exposure with the wafer and reticle actually set). Since the effects of multiple reflected light and stray light caused by the presence of light were not considered, a discrepancy occurred between the illuminance distribution measurement data and the light illuminance distribution during actual exposure.

This problem will be explained below with reference to FIGS. 6 and 7.

FIG. 6 shows the state of the light beam during actual exposure of a conventional reduction projection exposure system and the illuminance distribution of the main parts of the exposure optical system.

Figure 7 shows the state of the light beam, the illuminance distribution of the main part of the exposure optical system, and the light intensity distribution when the illuminance distribution of the corresponding area on the wafer surface is measured using a light receiver. .

In FIG. 6, 4a is the lens reflection surface of the condenser lens 4, 5a is the reflection surface of the reticle 5, and 6a is the reflection surface of the reduction lens 6.

Main light from the light source,! 19 is monochromatic light with high purity in order to correct the chromatic aberration of the reduction lens 6, and this principal ray 1
9 causes a standing wave effect on the wafer reflective surface 8a and is reflected,
This reflected light is re-reflected by the reduction lens reflective surface 6a, the reticle reflective surface 5a, the condenser lens reflective surface 4a, etc., and becomes multiple reflected light 20, a part of which gathers around the principal ray 19.

Furthermore, there is also the influence of the light intensity distribution 21.23 on the output side of the integrator 3 and the incidence of the reduction lens @7.

Even though the reticle surface illuminance distribution 22 is almost flat, the fifth substrate surface illuminance distribution 24 is stacked in the center thereof.

On the other hand, when determining the illuminance distribution, as shown in FIG. The amount of light accumulated at the center of the illuminance distribution 28 on the wafer surface is also smaller than the distribution 24 during actual exposure shown in FIG. 6.

As can be seen by comparing Figures 6 and 7, in the past there was a difference between the illuminance distribution data obtained using a light receiver and the illuminance distribution state during actual exposure due to multiple reflections. This causes a deviation. Furthermore, when the reticle is set and when it is not set, there is not much optical difference in the light intensity between the two under conditions where the light shielding rate of the reticle is low, but under conditions where the light shielding rate is high. There was a relatively large optical difference in the light intensity between the two.

By the way, in the field of semiconductor wafer manufacturing, which has become increasingly highly integrated in recent years, the flattening of the illumination distribution on the exposed surface affects the pattern line width accuracy and resist surface area in the photolithography process. There is an increasing demand for flattening the illuminance distribution. Therefore, there has been a need for a technique that allows the measurement of the illuminance distribution of the exposed area to be based on actual exposure, and for flattening the actual illuminance distribution of the exposed area with high precision based on this measurement data.

The present invention has been made in view of the above points, and its first purpose is to improve the reliability of the measurement by measuring the illuminance distribution of projection exposure that meets the conditions of actual exposure. The second objective is to flatten the illuminance distribution of the exposed object such as a process wafer with high precision, thereby improving the line width accuracy and linearity of the pattern formed on the exposed object. The purpose is to uniformize the reduction of the resist film.

[Means to solve the problem]

The first problem-solving means relates to an illuminance distribution correction method for achieving the above-mentioned first objective, and the contents thereof include a projection exposure device that transfers the original pattern of the redicle through an illumination optical system and an imaging optical system. In the method of measuring the illuminance distribution of the exposed surface by setting a photoreceiver sensitive to n-point light at a position corresponding to the exposed surface, the light receiving surface of the photoreceiver is set as the exposed object The method is characterized in that the illuminance distribution on the exposed surface is measured under the same light reflection conditions as on the physical substrate and with a pattern projection reticle actually attached.

The second problem-solving means relates to an illuminance distribution correction method for achieving the above-mentioned second objective, and the content thereof is to transfer the original pattern of the reticle onto the substrate via an illumination optical system and an imaging optical system. In a projection exposure apparatus that performs projection exposure, during actual projection exposure, a light receiver for measuring the exposure light illuminance distribution is set at a position corresponding to the exposed surface, and the light reflection conditions of the light receiving surface of this light receiver and the substrate are set. and measure the exposure light illuminance distribution at a position corresponding to the exposed surface using the light receiver with the reticle actually attached.
If there is a discrepancy between the measured illuminance distribution and the required illuminance distribution, an optical system filter for illuminance distribution correction is formed based on the measured illuminance distribution, and when performing projection exposure on the actual substrate. The method is characterized in that the illuminance distribution correction filter is set at an appropriate position on the optical path of projection exposure.

The third problem-solving means relates to an apparatus for implementing the illuminance distribution correction method of the second problem-solving means, and its contents include: a stage with a positioning adjustment mechanism for positioning a substrate to be exposed; In the apparatus comprising an illumination optical system and an imaging optical system for transferring a reticle pattern to the substrate, a light receiver for measuring the exposure light illuminance distribution at a position corresponding to the substrate surface is mounted on the stage, and the light receiver is means for setting the light receiving surface to be the same as the light reflection condition of the substrate, and monitoring the illuminance distribution measurement data detected by the light receiver; It is characterized by comprising an optical system filter that corrects the illuminance distribution to a desired distribution.

[Effect]

According to the first problem solving means, the exposure light illuminance distribution on the exposed object (substrate) in projection exposure is reduced to 7! When determining the amount of light, the reticle was actually set and the light receiving surfaces of the 11 light receivers were set to be the same as the light reflection conditions on the substrate, so the exposed surface could be adjusted without the substrate. Even when the illuminance distribution at the corresponding position is measured, it is possible to measure the same exposure light illuminance distribution as during actual exposure (at the time of actual projection illumination with the reticle and substrate set). That is, 1. As mentioned in the [Problems to be Solved by the Invention] section, during actual exposure, a part of the principal ray of the exposure light is reflected on the substrate (process wafer), and this is re-reflected by the reticle etc. Multiple reflected light occurs between the substrate and the reticle, and the - part overlaps with the principal ray, resulting in a region with high light intensity at the center of the illuminance distribution on the exposed surface of the substrate. In the present invention, by making the light-receiving surface of the photodetector that replaces the substrate the same as the light reflection conditions of the substrate, and by setting the reticle at the time of measurement, the substrate is This is because at least the multiple reflection phenomenon similar to that of blood loss light can be reproduced. Note that when measuring the illuminance distribution by actually wearing the reticle in this way, the reticle pattern will be included in the illuminance distribution, so when reading the data, it is necessary to smooth out the amount of light attenuation due to the presence of the pattern in advance. In addition, according to this measurement method, the illuminance distribution of the exposed area is measured by taking into account the influence of the light transmittance of the reticle material itself. becomes possible.

Then, if we use data from such illuminance distribution measurement,
If there is a portion to be corrected in the illuminance distribution, correction can be performed in accordance with the illuminance distribution of actual exposure.

This correction method is achieved by the second problem solving means.

That is, according to the second problem solving means, after the illuminance distribution is measured by the first problem solving means, it is found which part of the illuminance distribution should be corrected based on the measured illuminance distribution data, An optical system filter for illuminance distribution measurement is formed along this line. Specifically, this correction filter is made by, for example, applying a surface treatment to give a low transmittance at a position corresponding to the correction area using a light-transmitting plate, and then this correction filter is formed by projection exposure. By setting it at an appropriate position on the optical path of the system, parts of the illuminance region where the light is too strong are corrected to the set level. In particular, in the present invention, as described above, since the illuminance distribution is corrected using data of the exposure light illuminance distribution measured under the same conditions as actual exposure, it is possible to faithfully obtain a desired illuminance distribution, such as flattening the illuminance distribution.

Note that when performing correction to flatten the illuminance distribution on the exposed surface, for example, if the intensity of the illuminance distribution before correction is higher than the flat level in the central region, the illuminance distribution will be dimmed at the center. Although correction is performed by setting a filter such as the above on an appropriate optical path for projection exposure, the illuminance distribution may be tilted due to the influence of this correction filter. In this case, in addition to the original correction filter (first filter), a second filter formed to eliminate the slope of the illuminance distribution may be installed.
Since the filter corresponds to 31°32 of the embodiment of FIG. 1, please refer to the embodiment section for details.

Further, the device of the third problem-solving means is also specifically described in the embodiment, and its explanation here will be omitted.

〔Example〕

An embodiment of the present invention will be described based on FIGS. 1 to 3.

Fig. 1 is a block diagram of a reduction projection exposure apparatus to which this embodiment is applied, and an explanatory diagram of the light intensity distribution and light illuminance distribution of each main part of the exposure optical apparatus, and Figs. 2 and 3 show the light illuminance used therein. FIG. 3 is a diagram showing an optical filter for distribution correction.

In FIG. 1, the same reference numerals as those of the conventional apparatus shown in FIGS. 4 and 5 above indicate the same or common elements.

In other words, 1 is a condenser mirror, 2 is a mercury lamp serving as a light source, and 3 is a condensing mirror.
4 is an integrator, 4 is a condenser lens for illuminating the reticle 5 with uniform light, 5 is a reticle that becomes the original pattern, 6 is a reduction lens, 7 is an entrance pupil of the reduction lens, 8 is a process wafer coated with resist, 9 is a wafer chuck.

10 is a Z stage, 11 is a Y stage, and 12 is an X stage, and these elements are common to the conventional example.

Reference numeral 33 denotes a light receiver for measuring exposure light illuminance distribution, which is a main element of the present invention, and the light receiver 33 is mounted on the Z stage 1o so as to be located next to the wafer chuck 9. Light receiver 33
The light receiving surface is set to the same light reflection condition as the surface of the process wafer 8. Specifically, the light receiver 33
on the light receiving surface.

A light transmitting plate having the same light reflectance as the wafer 8 is placed on the wafer 8, or the light receiving surface itself is subjected to surface treatment so as to have the same light reflection conditions as the wafer 8.

In addition, in this embodiment, when performing actual exposure, an optical correction filter 31 is placed before (or after) the integrator 3 with the mercury lamp 2 as a reference, and an optical correction filter 31 is placed before the condenser lens 4. A filter 32 for use is arranged.

Therefore, in this embodiment, when measuring the illuminance distribution at positions corresponding to the eight surfaces of the wafer, the measurement is performed with the reticle 5 that will actually be used set.

In this case, the correction optical filters 31 and 32 are not set initially. Then, as shown in FIG. 1, the stage is controlled in the XY force direction so that the light receiver 33 is located in the light irradiation area of the projection exposure system, and the light receiving surface of the light receiver 33 is positioned above the wafer 8.
Z the stage so that it is at a height corresponding to the exposed surface.
The light illuminance distribution is measured by controlling the position in the direction.

According to such exposure light illuminance distribution training, reticle 5
is actually set, and the light receiving surface of the light receiver 33 is aligned with the wafer 8.
Since the light reflection conditions were set to be the same as that of
Even when the illuminance distribution of the projection exposure system is measured without the wafer 8, the exposure light illuminance distribution is the same as in the actual exposure shown in Figure 6 (actual projection exposure with the reticle 5 and wafer 8 set). can be measured. That is, during actual exposure, a part of the principal ray of the exposure light is reflected on the wafer 8, and this is re-reflected by the reticle reflective surface 58, etc. outside of the condenser lens reflective surface 4a and the reduction lens reflective surface 6a, resulting in multiple reflected light. , and the - part overlaps with the chief ray, so
Although a region where the light intensity is partially strong occurs at the center of the exposed area on the wafer 8, according to this embodiment, the exposure light illuminance distribution during actual exposure is reproduced and the exposure light illuminance distribution is measured. be able to.

This illuminance distribution measurement can be recognized, for example, by monitoring data based on the detection signal of the light receiver 33 on a CRT display or the like. Note that when monitoring the illuminance distribution of the exposed area, the pattern of the reticle 5 is actually included in the illuminance distribution, so read the illuminance distribution measurement data assuming a state where this pattern does not exist. There is a need. Therefore, in order to eliminate the influence of the dimming of the reticle pattern, the monitoring device is provided with a smoothing circuit for smoothing the dimming of the illuminance distribution caused by this pattern.

Then, based on this measurement data, the exposure light illuminance distribution at a position corresponding to the wafer surface is corrected. Specifically, first, the first filter 31 to be corrected is formed based on the monitored illuminance distribution measurement data. This filter 31 is for eliminating the bulge in the center of the illuminance distribution 24 during actual exposure shown in FIG. 6, which has already been described.As shown in FIG. 2, the light transmittance is lower at the center 42 than at the periphery 41. The light transmittance at the center 42 is determined based on illuminance distribution measurement data.

Due to the presence of this optical filter 31, the integrator 3
and the light intensity distribution on the entrance pupil 7 of the reduction lens 6 34.36
As shown in the figure, the distribution is concave in the center. In this case, the degree of concavity of the light intensity distribution is such that it cancels out the influence of multiple reflected light generated between the light receiver (wafer equivalent surface) 33, which is assumed to be the surface of the reticle 5 to the wafer 8, on the exposure light illuminance distribution of the wafer itself. In other words, the concavity of this light intensity distribution is the exposure light illuminance distribution 2 of the actual exposure time phase light in Fig. 6.
This offsets the rise in light intensity that occurs near the center of 4.

However, when the filter 31 is attached to the projection exposure system, if its accuracy is poor, adjustments cannot be made in delicate areas, and the illuminance distribution 35 on the surface of the reticle 5, as well as the wafer 8 equivalent ifi,i,
The illuminance distribution 37 of No. 1 has a slope as shown in the figure.

In this embodiment, a second correction filter 32 is provided above the condenser lens 4 in order to correct this 1-) slope of the illuminance distribution.

The correction filter 32 is a glass plate as shown in FIG.
As shown by reference numeral 38, it is set to have a slope that cancels out the slopes of the illuminance distributions 35 and 37.

Note that the filter 31 may be formed by, for example, depositing chromium on a glass plate so as to have a transmittance depending on the situation at the time, or alternatively, forming a portion where the transmittance should be low into a frosted glass shape.
The filter 32 for correcting the illuminance gradient is formed by gradually changing the concentration distribution of chromium vapor/deposition.

Therefore, in this embodiment, since the exposure light illuminance distribution of the actual exposure time phase light of the process wafer can be monitored, the measurement accuracy of the exposure light illuminance distribution is improved, and the light distribution is further corrected based on the measurement data corresponding to this actual exposure. As a result, a flat wafer surface illuminance distribution suitable for actual exposure can be obtained.

As a result, the line width accuracy and linearity of the semiconductor wafer can be improved, and the reduction of the I-nodist film in the field can be made uniform, so it can be used regardless of the type of device such as memory, image sensor, etc. A high product yield can be obtained.

〔Effect of the invention〕

As described above, according to the present invention, firstly, the illuminance distribution of projection exposure that meets the conditions of actual exposure can be measured and the reliability of the measurement can be improved, and secondly.

By precisely flattening the illuminance distribution of the exposed object such as a process wafer, the line width accuracy and linearity of the pattern formed on the exposed object (substrate) can be improved, and the resist surface area'
It is possible to improve the product quality by making the process more uniform.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an apparatus showing an embodiment of the present invention, FIGS. 2 and 3 are explanatory diagrams of an optical correction filter used in the above embodiment, and FIG. 4 is a diagram of a conventional reduction projection exposure apparatus. Diagram,
Fig. 5 is an explanatory diagram of conventional exposure light illuminance distribution measurement, Fig. 6 is an explanatory diagram showing the light beam condition during conventional actual exposure, light intensity and illuminance distribution in the main part of the optical system, and Fig. 7 is an explanatory diagram of conventional exposure light illuminance distribution measurement. FIG. 3 is an explanatory diagram showing a light beam state, light intensity, and illuminance distribution at the time of measuring the light illuminance distribution. DESCRIPTION OF SYMBOLS 1... Condenser mirror, 2... Mercury lamp, 3... Integrator, 4... Condenser lens, 5... Reticle, 6... Reduction lens, 7... Entrance pupil, 8...・・・
Base @ (process wafer), 10, 11. 12... stage, 31. 32... correction filter, 33 light receiver. Figure 1 Figure 2 Figure 3 Figure Figure Figure Figure Figure

Claims (1)

[Claims] 1. A light receiver sensitive to exposure light is set at a position corresponding to the exposed surface of a projection exposure device that transfers the original pattern of the reticle via an illumination optical system and an imaging optical system. In this method of measuring the illuminance distribution of the exposed surface using this light receiver, the light receiving surface of the light receiver is set to the same light reflection conditions as the substrate that is the exposed object, and the reticle is actually attached. . A method for measuring illuminance distribution on a surface to be exposed in projection exposure, characterized in that the illuminance distribution on the surface to be exposed is measured. 2. In the first aspect, a plate is placed on the light receiving surface of the light receiver to create the same light reflection conditions as on the substrate, or the light receiving surface itself is brought into the same state as the light reflection conditions on the substrate. A method for measuring illuminance distribution on the exposed surface of projection exposure using surface treatment processing. 3. In a projection exposure apparatus that projects and exposes the original pattern of a reticle onto a substrate via an illumination optical system and an imaging optical system, a light receiving device for measuring the exposure light illuminance distribution is placed at a position corresponding to the exposed surface during actual projection exposure. With the light receiving surface of this light receiver set to the same light reflection conditions as on the substrate, and with the reticle actually attached, the light receiver measures the exposure light illuminance distribution at a position corresponding to the exposed surface. measure,
If there is a discrepancy between the measured illuminance distribution and the required illuminance distribution, an optical system filter for illuminance distribution correction is formed based on the measured illuminance distribution, and when performing projection exposure on the actual substrate. A method for correcting illuminance distribution on an exposed surface in projection exposure, characterized in that the illuminance distribution correction filter is set at an appropriate position on the optical path of projection exposure. 4. In the third aspect, the projection exposure apparatus is a reduction projection exposure apparatus, and the illuminance distribution correction filter has a position on the entrance pupil of the reduction projection lens that can change the light intensity distribution, and a reticle. These filters are set at positions where they can change the illuminance distribution on the surface, and by changing the light intensity distribution on the entrance pupil of the reduction lens and the illuminance distribution on the reticle surface, the illuminance distribution on the substrate can be changed. A projection exposure illuminance distribution correction method for the exposed surface. 5. In the third or fourth claim, the filter for illuminance distribution correction is a plate having light transmittance, and a surface treatment that provides low transmittance is applied to a position corresponding to the correction location according to the degree of correction. A method for correcting illuminance distribution on an exposed surface for projection exposure. 6. In an apparatus comprising a stage with a positioning adjustment mechanism for positioning a substrate to be exposed, and an illumination optical system and an imaging optical system for transferring a reticle pattern to the substrate, exposing the stage at a position corresponding to the substrate surface. means for mounting a light receiver for measuring light illuminance distribution, setting the light receiving surface of the light receiver to be the same as the light reflection condition of the substrate, and monitoring illuminance distribution measurement data detected by the light receiver; 1. A projection exposure apparatus comprising: an optical system filter that corrects the illuminance distribution of an exposed surface to a desired distribution based on illuminance distribution measurement data. 7. In the sixth aspect, the means for monitoring the illuminance distribution measurement data takes into consideration that the pattern of the reticle is included in the measured illuminance distribution, and calculates the attenuation of the illuminance distribution due to the presence of the reticle pattern. A projection exposure device that has a smoothing processing function for smoothing. 8. In claim 6 or 7, the projection exposure apparatus is a reduction projection exposure apparatus, and the optical system filter for correcting the illuminance distribution corrects the light intensity distribution on the entrance pupil of the reduction lens. A projection exposure apparatus is composed of a filter, a filter for correcting the illuminance distribution on the reticle surface, etc., and is set so that the illuminance distribution directly above the substrate is finally corrected through these filters.